#region Copyright notice and license

// Copyright 2015 gRPC authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

#endregion

using System;
using System.Threading;
using System.Threading.Tasks;

using Google.Apis.Auth.OAuth2;
using Grpc.Core;
using Grpc.Core.Utils;

namespace Grpc.Auth;

/// <summary>
/// Factory/extension methods to create instances of <see cref="ChannelCredentials"/> and <see cref="CallCredentials"/> classes
/// based on credential objects originating from Google auth library.
/// </summary>
public static class GoogleGrpcCredentials
{
    /// <summary>
    /// Retrieves an instance of Google's Application Default Credentials using
    /// <c>GoogleCredential.GetApplicationDefaultAsync()</c> and converts them
    /// into a gRPC <see cref="ChannelCredentials"/> that use the default SSL credentials.
    /// </summary>
    /// <returns>The <c>ChannelCredentials</c> instance.</returns>
    public static async Task<ChannelCredentials> GetApplicationDefaultAsync()
    {
        var googleCredential = await GoogleCredential.GetApplicationDefaultAsync().ConfigureAwait(false);
        return googleCredential.ToChannelCredentials();
    }

    /// <summary>
    /// Creates an instance of <see cref="CallCredentials"/> that will use given access token to authenticate
    /// with a gRPC service.
    /// </summary>
    /// <param name="accessToken">OAuth2 access token.</param>
    /// <returns>The <c>CallCredentials</c> instance.</returns>
    public static CallCredentials FromAccessToken(string accessToken)
    {
        return CallCredentials.FromInterceptor(GoogleAuthInterceptors.FromAccessToken(accessToken));
    }

    /// <summary>
    /// Converts a <c>ITokenAccess</c> (e.g. <c>GoogleCredential</c>) object
    /// into a gRPC <see cref="CallCredentials"/> object.
    /// </summary>
    /// <param name="credential">The credential to use to obtain access tokens.</param>
    /// <returns>The <c>CallCredentials</c> instance.</returns>
    public static CallCredentials ToCallCredentials(this ITokenAccess credential)
    {
        return CallCredentials.FromInterceptor(GoogleAuthInterceptors.FromCredential(credential));
    }

    /// <summary>
    /// Converts a <c>ITokenAccess</c> (e.g. <c>GoogleCredential</c>) object
    /// into a gRPC <see cref="ChannelCredentials"/> object.
    /// Default SSL credentials are used.
    /// </summary>
    /// <param name="googleCredential">The credential to use to obtain access tokens.</param>
    /// <returns>>The <c>ChannelCredentials</c> instance.</returns>
    public static ChannelCredentials ToChannelCredentials(this ITokenAccess googleCredential)
    {
        return ChannelCredentials.Create(new SslCredentials(), googleCredential.ToCallCredentials());
    }
}
